Bibliography
To find my background information I used:
- My AQA biology coordinated award book
- My notes from class
I have to keep the pH and temperatures the same throughout the experiment otherwise the enzymes will denature. Extreme pH level also makes the enzyme denature. Catalase has an optimum temperature of about 30ºC and an optimum pH of 7.
Identifying variables
Enzymes can be affected by the conditions they are in, these conditions are:
- PH (must stay the same for this reaction)
- Temperature (must stay the same, see above for details)
- Enzyme concentration (is what I will be varying)
- Substrate concentration (must stay the same in this reaction)
- Enzyme Volume (must stay the same in this reaction)
- Substrate Volume (must stay the same in this reaction)
- Inhibitors (none where added in this experiment)
In my experiment the independent variable is the Enzyme concentration, which means I will have to try and keep all the other variables constant.
PH
The pH must be right for each enzyme. If the pH is too acidic or too alkaline then the enzyme will be affected. Every enzyme works best at a different optimum pH, catalases works best at a pH of 7. pH is so important that at the wrong pH the enzyme can be denatured.
Temperature
Temperature is one of the most important factors of this experiment as if the temperature is too high, the enzymes will denature. If the temperature is too low the enzymes will not be able to move fast enough to collide. As the temperature increases, the molecules move faster, this is known as kinetic theory. In an enzyme catalysed reaction, like this one, this increases the rate at which the enzyme and substrate molecules collide and therefore the rate of the reaction. As the temperature rises the hydrogen and ionic bonds, which hold the enzyme molecules in shape, break. If the shape is deformed, the enzyme work as the active site no longer accommodates the substrate. The enzyme is denatured.
Enzyme Concentration
The independent variable in this experiment is the concentration of the enzyme catalase. For the highest rate of reaction there should be the highest concentration of enzymes. At the start of the experiment the reaction should be slow as there are lots of substrates but not many enzymes. The rate should increase, as the concentration gets higher until it will eventually level off. This will happen when the number of enzymes outnumbers the number of substrates. I varied the enzyme concentration by diluting the enzyme with water. I used the percentages 2%, 4%, 6% and 10% of the enzyme. (see the dilution table in the pilot study)
Substrate Concentration
The amount of product produced depends on the concentration of the substrate so if there is a high substrate concentration then more product will be produced and so the rate of reaction will also increase. If there is a low substrate concentration, less product will be produced. The substrate concentration can be put as high as you like but beyond a certain point the rate of reaction cannot get any higher. This will be the maximum speed of reaction.
Enzyme Volume and Substrate Volume
Both enzyme volume and substrate volume will be kept the same for this experiment. This was at 5cm³ for each test. Although I made up my concentrations with 50cm³.
Time
The time for the complete breakdown of the hydrogen peroxide for the 5 different concentrations is the dependant variable. This mean that, that is the one I will be measuring.
Hypothesis’s
I predict that as the enzyme concentration (catalase) increase; the rate of reaction will also increase. This is because the time taken for the hydrogen peroxide to break down will decrease, thus increasing the rate of reaction. I also predict that the rate of reaction and concentration of enzyme will be directly proportional to the amount of enzyme, until they get to a point were the enzyme will have denatured.. I based my hypothesis on the lock and key theory and the collision theory. As the higher the enzyme concentration is the more collision will occur and the faster the rate of reaction will be.
Pilot Study
Firstly I did a pilot study, by recording data for 2% and 10% enzyme concentration. I needed to dilute the enzyme to only two concentrations using the dilution table. I used this table also for the actual experiment. The data I obtained from this investigation has been recorded in a table showing the time, enzyme concentration and rate of reaction.
Outline Method
After I had done my pilot study (results shown on previous page) I decided to use the concentrations 2%, 4%, 6% and 10% for my main experiment. I First got 5 beakers ready to put my different concentrations in. I made up my concentrations by using the dilution table (below). I made up 50mls of each solution. I used 5cm³ of each one for each experiment. I used each concentration twice and so got two sets of results. I was already supplied with 10% catalase (yeast), so that concentration did not need to be made up.
Dilution table
I used a gas syringe for my experiment. 5cm³ of hydrogen peroxide was put into a tall necked beaker at the start of each experiment. 5cm³ of yeast was then added and the time was recorded.
Obtaining evidence
Apparatus
- 5 beakers
- 10 long-necked beakers
- Stirring rod
- Gas syringe
- Permanent Marker
- Bungs
- Test tubes
- Stopwatch
I could have used a data logger instead of the gas syringe.
Method
Apparatus
Firstly I got out of the apparatus I need.
I marked each beaker with the concentration that were to be put in it.
I then made up the concentrations using the diluting table.
I then set up the gas syringe.
I choose this piece of equipment as I thought it would be easier to do the experiment manually as computers are known to be unreliable.
I regret this choice now.
Each of the 5 beakers then contained the concentrations 2%, 4%, 6%, 8% and 10% yeast.
I made sure the yeast had been stirred before putting 5cm³ of each concentration in.
I did two tests for each concentration.
I recorded data every 5 seconds.
At the end of each test I had to make sure I had pushed the gas syringe back to the start.
I also had to make sure the yeast had been stirred before I started the next test.
I had to make sure that as soon as the yeast was added the bung was put on, so to let the least amount of gas escape, I also had to make sure the stopwatch was started at the right time.
These are the results I got for my experiment.
I drew a graph for initial rates as well. I needed to find the reliability for my results. I did this by talking the highest initial rate and lowest initial rate for each concentration. I did the highest minus the lowest and then divided that by the highest. The results are overleaf.
This shows that the data collected was not very reliable. There are quite a few reasons why this could be. One is that the data was not collected on the same day and was therefore not collected at the same temperature.
Evaluation
My graphs fitted with my hypotheses. They showed how as the concentration went up the rat also went up. Its shows how the collision theory is correct, as the more enzyme concentration there is the faster the reaction is. This is because as the enzyme concentration goes up, there are more molecules that collide with each other and so the rate of reaction is faster. There didn’t seem to be any obvious anomalous results, as most of the results seemed wrong. This could be due to the fact the tests were done on 3 separate days and on all these day there was different temperatures. There was also the problem of reaction time, as it took time to get the bung on once the yeast was put in, as well as the time it took from when it was put in to when the stopwatch was started. There were also delayed reactions between when you shout NOW to when the other person says the amount and when you write it down. These problems could have been sorted out by using a data logger, this would have also produced graphs, which would have been more accurate than hand drawn ones. I think that if I did this experiment again I would do more than 3 tests for each concentration to ensure I got better results. I would also try and do all my tests on the same day, so there was the same temperature. I would also use a buffer, this would ensure that the pH was kept at 7 for the whole experiment.